(34 



MISCELLANEOUS NOTES'. 



topore. When the latter becomes horse-shoe shaped, this area is enclosed 



within it and becomes 



Pig. 



Mcso 



nnnum 



E 



Yk. Plug 



Mes». 



ICCX JTyp. 



F 



yk. Plug;. 



Hyp. 



1). Transverse, section through the line AB, E. Longi- 

 tudinal, seetiou through the line X Y, in fig. 2 A. 

 F. Interpretation of the section E. 



easily noticeable (fig. 

 2, A). Transverse and 

 longitudinal sections 

 through the spot in 

 question are as in fig. li 

 In Contrib. I, Ishikawa 

 and the author have 

 identified this epiblast- 

 free mass with the yolk- 

 plug of the Amphibian 

 ovum. The structure 

 has also been noted by 

 other writers, and its 

 theoretical significance 

 has been interpreted in 

 various ways. The 

 author, in the present 

 Contribution, follows 

 the fate of this " yolk- 

 plug " stage by stage 

 in three species of 

 Chelonia, Trionyx 

 japon teas, Clcmmys 

 japonica, and Chelonia 

 capuana. 



When the medullary folds arise and reach the posterior portion of 

 the embryonic shield, they embrace the yolk-plug between then- 

 posterior ends as in a vice, and compress it laterally, thus lifting it up to 

 the level of their dorsal surface. The yolk-plug meanwhile keeps its 

 own independence. 



The yolk-plug now apparently recedes leaving in its track a groove 

 from which the cells are proliferated. This movement backward of the 

 yolk-plug is believed by the author to be caused by the active prolifera- 

 tion of cells from the lateral blastopore lips, while pressing to meet each 

 other in the median line. As cells thus proliferated accumulate, they 

 form a mass which necessarily pushes the yolk-plug backwards. This 

 pushing goes on, until the yolk-plug is placed at about the edge of the 



